1. Field of the Invention
The present invention relates to monitoring and positioning of interference sources, base stations and users in wireless networks.
2. Description of the Related Art
In wireless networks there exists interference which can originate from different sources. Interference sources can be base stations used by other networks, video devices, malfunctioning microwave ovens, baby alarm devices and any other devices which use the same frequency band with the used radio links. There is a need to monitor and detect the interference sources quickly in order to ensure good quality for the data traffic in the network.
In prior art, interference sources have been detected by mostly manual measurement configurations. One solution in prior art uses a measurement computer (PC), appropriate spectrum analyzing software, WLAN card and a separate beam antenna. In this configuration, the beam antenna has been connected to the antenna port of the measurement computer. The antenna is manually held e.g. in the hand of the user and by rotating the antenna, the interference magnitude in different directions is found out. The PC and the spectrum analyzing software can be replaced by a complete spectrum analyzer. One problem in such a solution is that the measurement must be performed manually which increases the error of the measurement. Furthermore, the interference, which is present only occasionally, is practically untraceable by such a device. Also the measurement requires much time and requires a lot of effort. In practice this procedure is performed after the network user has reported bad connection quality to the administrator. It is also difficult to find WLAN cards which could be used with an external antenna and with a spectrum analyzing software in a laptop computer.
Furthermore in prior art, wireless intrusion detection prevention system (WIDPS) has been developed. The WIDPS includes measurement stations which have a capability to measure the RF signal level and the overall noise level. The WIDPS system includes security monitoring stations using omnidirectional antennas which can detect the signal or interference level in different measurement stations. The positioning of the signal or interference sources is based on the measured signal level at each of multiple stations and the location of the interference source is estimated therefrom. The WIDPS requires a vast amount of monitoring stations in the network area in order to work properly. A problem in the WIDPS solution is that the system doesn't work with ad hoc measurements in a network which does not include the WIDPS system itself. The WIDPS further includes a rather advanced installing procedure in order to teach the apparatus to locate the interference sources properly. Furthermore, WIDPS monitoring stations with omnidirectional antennas cover clearly smaller area than stations with directive antennas providing signal level amplification often in the range of 7-15 dB. It is worth noticing that 6 dB antenna gain doubles cell radius in open space. Finally, the elevation of the interference source can't be located unless measurement stations are placed both in an upper and lower location as viewed from the interference source.
One known solution is the base station network which uses omnidirectional antennas and which is directed by WLAN switches. In principle, the positioning of the interference sources and other signals is performed as in the WIDPS described above. In addition to limitations already mentioned, a problem in such a solution is that it works only with WLAN switches provided by one manufacturer and with the corresponding base station supported by the switches.